In many clinical situations, blood vessels are occluded for a variety of purposes, such as to control bleeding, to prevent blood supply to tumors, and to block blood flow within an aneurysm. Vaso-occlusive devices have been used in the treatment of aneurysms. Vaso-occlusive devices are surgical implants placed within blood vessels or vascular cavities, typically by the use of a catheter, to form a thrombus and occlude the site. For instance, an aneurysm may be treated by introduction of a vaso-occlusive device through the neck of the aneurysm. The thrombogenic properties of the vaso-occlusive device cause a mass to form in the aneurysm and alleviate the potential for growth of the aneurysm and its subsequent rupture. Other diseases, such as tumors, may also be treated by occluding the blood flow to a target area.